1. Field of the Invention
The present invention relates to the transport and processing of semiconductor wafers, and in particular to a system wherein a wafer handling robot includes mechanisms for gripping and removing pod and port doors from an I/O port of a SMIF minienvironment, and storing the doors at a convenient location within the minienvironment during wafer transfer through the port.
2. Description of Related Art
A SMIF system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient environment do not enter the immediate wafer environment.
A SMIF system has three main components: (1) minimum volume, sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a miniature clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassette between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to particulates. Further details of one proposed SMIF system are described in the paper entitled xe2x80x9cSMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,xe2x80x9d by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111-115.
Systems of the above type are concerned with particle sizes which range from below 0.02 microns (xcexcm) to above 200 xcexcm. Particles with these sizes can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half xcexcm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 xcexcm substantially interfere with 1 xcexcm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor processing geometries which today in research and development labs approach 0.1 xcexcm and below. In the future, geometries will become smaller and smaller and hence smaller and smaller contamination particles become of interest.
There are in general two types of SMIF pods: front opening and bottom opening. A front opening SMIF pod generally comprises a cover which may either be adapted for housing a wafer cassette, or may include shelves for supporting the wafers directly therein without a wafer cassette. The front opening pod further comprises a vertically oriented door mating with the cover. A bottom opening SMIF pod generally comprises a cover mating with a door located on a bottom surface of the pod. In order to transfer wafers and/or a wafer cassette from within the SMIF pod to within an I/O minienvironment on a processing tool, a door of the pod is supported on an I/O port of the minienvironment. The pod is designed so that the pod door overlies a port door covering the I/O port of the minienvironment, and the pod cover overlies a port plate surrounding the port door. Once located at the I/O port, mechanisms within the port door release and separate the pod door from the pod cover. Thereafter, the port door and pod door are brought into the I/O minienvironment, and moved together either up, down, or to the side of the minienvironment port to clear a path for the wafers and/or cassette to be transferred through the port. While the port and pod doors are retracted within the minienvironment, the pod cover generally remains affixed to the I/O port to prevent contaminants from entering the minienviromnent.
As shown in FIG. 1, and as previously indicated, after the pod door 20 is separated from the pod cover 22, the pod door 20 and the port door 24 are moved in a first direction into a minienvironment 26 by a first transport 27, and then moved in a second direction out of the path of the incoming wafers by a second transport 28. The pod and port doors may be moved upward once located within the minienvironment as shown in FIG. 1. Alternatively, the minienvironment 26 may be configured to move the pod and port doors downward, or to the sides of the port. Transport mechanisms having two degrees of freedom are known for moving the pod and port doors in the two directions (i.e., into the minienvironment and then out of the path the wafers).
Typically, once the port and pod doors have been moved out of the wafer path, a wafer handling robot within the minienvironment transfers the wafers and/or wafer cassette from the SMIF pod into the minienvironment. Once in the minienvironment, the wafers are generally transferred directly into the process tool. Although there are various known robot configurations, one such wafer handling robot 32 for accessing and transferring wafers is shown in FIG. 1. The robot 32 includes a shaft 36 mounted for rotation and translation along a z-axis concentric with the shaft axis of rotation. The robot 32 further includes a first arm 38 affixed to an upper end of shaft 36 for rotation with the shaft, and a second arm 40 pivotally attached to the opposite end of the first arm 38. The wafer handling robot further includes an end effector 42 pivotally attached to the second arm 40. The robot 32 is controlled by a computer (not shown) such that end effector 42 slides into the wafer cassette underneath one of the wafers, rises up to support the wafer, and thereafter retracts from the cassette with the wafer supported thereon. Additionally, multiple end effectors are known which employ a plurality of tines for simultaneously removing a plurality of wafers from a cassette. Alternatively, the wafer handling robot may grip the entire cassette from the top, bottom or sides of the cassette to transfer an entire batch of wafers within the pod into the minienvironment.
Having to position the removed pod and port doors either above, below, or to the sides of the I/O port of the minienvironment presents several drawbacks. First, semiconductor process tools and I/O minienvironments typically include more than one port. Having to leave space adjacent the I/O ports for positioning the removed pod and port doors limits the configuration of the minienvironment with respect to where the I/O ports may be located. For example, in the minienvironment of FIG. 1, the second I/O port (not shown) could not be positioned above the shown I/O port, as room must be left at that location for storing the pod and port doors during processing of a wafer lot within the processing tool. Additionally, a mechanical transfer mechanism must be provided at the front interior of the minienvironment for pulling the removed port and pod doors into the minienvironment, and another mechanical transfer mechanism must be provided for next translating the pod and port doors away from the I/O port. These transfer mechanisms are cumbersome, taking up valuable space at the front interior of the minienvironment, and also add to the complexity of the design and software control of the minienvironment. Furthermore, these transfer mechanisms are a potential source of contamination within the minienvironment.
It is therefore an advantage of the present invention to provide a minienvironment wherein the removed port and pod doors may be located at any convenient location within the minienvironment.
It is a further advantage of the present invention to provide a minienvironment where conventional transport mechanisms for pulling the pod and port doors into the minienvironment, and for translating the pod and port doors away from the I/O port may be omitted.
It is another advantage of the present invention that the wafer handling robot also accomplishes removal and storage of the port and pod doors to allow transfer by the robot of the wafers through the I/O port.
It is a further advantage of the present invention to simplify and provide greater flexibility with regard to the design of the electrical power supply and signal transfer for controlling the transfer of the port door to and from the I/O port.
It is a still further advantage of the present invention to reduce the sources of potential contamination within the minienvironment.
These and other advantages of the present invention are provided by a system within an I/O minienvironment, the system engaging a port door from within an I/O port, removing the port door and pod door coupled thereto, and setting down the pod and port doors at a convenient location within the I/O minienvironment. After wafer processing has been completed and the wafers have been transferred back through the I/O port to the SMIF pod, the system may retrieve the port and pod doors, and return the port and pod doors to their sealing positions within the I/O port and pod, respectively.
In a preferred embodiment, the system for gripping and transporting the port and pod doors may be located on the back end of the end effector of the wafer handling robot within the I/O minienvironment. The back end of the end effector is the end of the end effector opposite that used to transport the wafers and/or cassette.